The present invention relates in general to magnetic brush development apparatus for applying developer material to a latent image in an electrostatographic reproduction apparatus, and more particularly to an improved magnetic brush development apparatus including a device for facilitating measurement of toner level.
Magnetic brush development apparatus for applying developer material to a latent image in an electrostatographic reproduction apparatus are well known in the art. Such apparatus may include a housing having a sump Portion which contains a supply of developer material. When the developer material comprises a mixture of magnetic carrier particles and smaller pigmented marking particles, the material in the sump is agitated to triboelectrically charge the material prior to delivering it to a magnetic brush where it can be brought into association with, and transferred to, an electrostatic latent image to develop such image.
Copending, commonly assigned U.S. patent application Ser. No. 597,323, filed Apr. 6, 1984 U.S. Pat. No. 4,887,132 in the names of Joseph et al, and U.S. Patent No. 4,671,207, issued Jun. 9, 1987, in the name of Hilbert disclose magnetic brush development apparatus particularly suitable for use with developer material having pigmented marking particles and permanent magnetic carrier particles, such as disclosed in U.S. Pat. No. 4,546,060, issued Oct. 8, 1985, in the names of Miskinis et al. More particularly, the disclosed apparatus include a ribbon blender that is used for agitating (mixing), feeding and triboelectrically charging such material in the sump portion of a magnetic brush development apparatus, and a feed mechanism that delivers material from the sump portion to a magnetic brush. The ribbon blender is constructed to provide uniform flow distribution of developer material across the length of the apparatus so that a sufficient supply of material is delivered to the magnetic brush over its full extent to develop the entire latent electrostatic image.
Since the pigmented marking particles are used during image development, replenishment of the developer material must be periodically effected. Typical replenishment devices include a reservoir for replenishment material with a flow communication path between the reservoir and the sump of the of the development apparatus. A selectively actuable member, such as a roller, controls flow of replenishment material through the path. It has been found that under certain conditions measurement of level of replenishment material in the reservoir is inconsistent, which can result in running out of replenishment material without knowing it.